1. Field of the Invention
This invention relates to a coded aperture imaging system having a reconfigurable coded aperture mask, especially to an imaging system having adjustable imaging performance without requiring moving parts and to coded aperture imaging apparatus for operation at ultra violet, visible and infrared wavelengths.
2. Discussion of Prior Art
Optical systems for observing scenes are employed in a wide range of situations from CCTV security systems to surveillance/reconnaissance systems. Often these systems are required to be such that the imaging performance of the system can be adjusted, for example, in terms of resolution or image update rate. Another example is where there is a requirement for the imager to be scanned over a large field-of-regard (FOR) the FOR being many times larger than the instantaneous field-of-view (FOV).
Mechanical scanning of optical systems is well known, for instance movement of a lens or a mirror arrangement can change the FOV in the FOR or the whole imaging system may be moved. However movement of optical components requires generally bulky and heavy mechanical moving means and in some applications minimising size and weight are important. Further mechanically scanned systems can generate unwanted vibrations which can distort the acquired image. Also rapid movement of large and heavy optical components or the whole system, which can have a large moment of inertia, can be problematic.
It is also known to a use a spatial light modulator (SLM) to display a diffractive pattern with a detector array so as to achieve a scanning imaging system, see for example published PCT application WO2000/17810. Different diffractive patterns can be displayed which direct radiation from different parts of the scene to a detector. Thus scanning is achieved without any moving parts which can reduce the weight and bulk of the optical system. Such diffractive optics are usually useful over a narrow band (monochromatic), as they are highly dispersive. They are often inefficient too.